As a model system for investigating the feasibility of performing genetic engineering in humans, we will insert normal alleles into the cells of mice with hereditary anemias. The recipient cells will be from: (1) alpha thalassemic mice, Hba(th-J)/+ with a deletion on Chromosome 11 that includes the adult and embryonic alpha globin genes; and (2) mice homozygous for mutations at the W locus on Chromosome 5 with a macrocytic anemia that is cured by injections of normal stem cells. In experiment 1, we will study the effects of introducing a human alpha globin gene into alpha thalassemic mice. The human alpha globin gene was integrated into the genome of a +/+ mouse, microinjected as a zygote. The recipient has passed the human gene on to her wild-type and alpha thalassemic progeny. We will study human alpha globin gene expression in the thalassemic and normal progeny. In experiment 2, we will transfect normal alleles into the pluripotential stem cells from Hba(th-J)/+ mice or from mice carrying mutations at the W locus. We will enrich the mutant stem cells, transfect them with normal alleles and a selectable marker, selectively expand the cells in vitro, and inject the cells back into the mutant mice. In experiment 3, we will generate mutant (Hba(th-J)+, Hba(th-J)/Hba(th-J), W41/W39, etc.) totipotent teratocarcinoma cells and microinject them with normal alleles. We will produce tetraparental mice by inserting the mutant teratocarcinoma cells bearing normal alleles into W41/W39 blastocysts. W41/W39 blastocysts will be used because their cells will not compete with cells from the alpha thalassemic teratocarcinomas or from the "cured" W41/W39 teratocarcinomas to populate the erythrypoietic organs.